Partial collimation of a bright point light source, for example a Light Emitting Diode (LED) or High Intensity Discharge (HID) lighting, is generally achieved using in-line optics usually consisting of a lens or a reflector. Hand torch lights and car headlights often use parabolic reflectors, convergent lenses or a combination of the two. Spot lights such as those found in ceilings tend to use total internal reflection optics using a solid parabolic lens made of polymethyl methacrylate or glass.
In the case of a car headlight, limitations exist as to how large the partially collimated beam can be made. A large headlight requires commensurately sized collimating optics and as its aperture size increases it becomes deeper, thereby intruding into the under bonnet space which is generally quite limited.
A virtual or artificial skylight is similarly constrained in that its depth dictates the spaces into which it can fit. A skylight of shallow depth can conceivably fit into more ceiling spaces than a deeper one. The Applicant's International Patent application number WO2017048569 describes a compact artificial skylight which can be installed within a typical ceiling cavity such that they can be installed in office spaces or other rooms without natural ambient light. The artificial skylight described in WO2017048569 generally includes at least one light source, at least one first collimator, a prism sheet, and at least one transmissive material. The at least one first collimator is configured to collimate light from the at least one light source. The prism sheet is disposed adjacent to the at least one first collimator and is configured to reflect and refract collimated light received from the at least one first collimator. The at least one transmissive material is disposed adjacent to the prism sheet and is configured to radiate light diffusely.
Embodiments of the present invention seek to provide a new and alternative artificial skylight to the arrangement proposed in WO2017048569 which may, for example, provide an even more compact artificial skylight, and also improve the appearance of the artificial sky.